An optical system includes an optical device that is based on interference between optical signals having a phase difference. Interference, as used herein, refers to, for example, the addition or superposition of two or more optical signals. Such optical devices include an optical splitting device for splitting an optical signal at any ratio, and a Mach-Zehnder optical modulator.
FIGS. 22 and 23 illustrate optical splitting devices for providing an arbitrary splitting ratio. At least one of two waveguides 100 and 101 arranged between two 2:2 optical couplers 105 and 106 includes a phase shifter region causing a phase difference between split optical signals.
As illustrated in FIG. 22, phase shifter regions 102 and 103, narrowed in the waveguide width, are respectively arranged on the two waveguides 100 and 101. The two phase shifter regions 102 and 103 are thus different in waveguide shape. A splitting ratio is provided on such an optical splitting device by adjusting the length of a linear narrow-width waveguide section of the one phase shifter region 102 or by adjusting a taper angle of a tapered waveguide section of the other phase shifter region 103.
The optical splitting device FIG. 23 includes a phase shifter region 104 having a width-tapered section on part of one waveguide 101, out of the two waveguides 100 and 101. An arbitrary splitting ratio can be provided on such an optical splitting device by adjusting the length or the taper angle of the width-tapered section of the waveguide in the phase shifter region 104.